1. Field of the Invention
This invention relates to a magnetic powder composed of particles suitable for forming a magnetic layer of a coating-type magnetic recording medium such as a magnetic tape or magnetic disk, particularly to a magnetic powder whose catalytic action is inhibited even when composed of fine particles.
2. Background Art
Magnetic recording media are today desired to have not only enhanced recording capacity but also improved reliability and durability. An intense effort is therefore underway to boost the recording capacity of next-generation magnetic recording media by using short wavelength signals to realize high recording density. The achievement of this goal will require a magnetic powder consisting of fine particles and exhibiting excellent properties. Unless the particle size is much smaller than the length of the region for recording the short-wavelength side signal, a distinct magnetic transition cannot be produced, making practical recording impossible. The particle size of the magnetic powder is therefore required to be sufficiently small.
To realize higher recording density, the resolution of the recording signal must be increased. Reduction of magnetic recording medium noise is therefore important. Noise is usually attributable to particle size and tape surface property. The finer the particles and the smoother tape surface, the lower the noise becomes. This also makes it necessary for a magnetic powder used for high density recording to have sufficiently small particle size.
On the other hand, the importance of avoiding damage to stored data increases with increasing storage capacity of the magnetic recording medium. A tape or the like for data storage is therefore required to have enhanced reliability. A tape with improved storage stability is therefore desired.
In light of these circumstances, acicular magnetic powders for magnetic recording media have been developed that are composed chiefly of Fe and consist of particles having an average major axis diameter of 70 nm or less (see JP 2002-289415A, for example).
A coating material formed using a magnetic powder experiences declines in stability and storability with decreasing average particle diameter of the magnetic powder. A magnetic tape produced using the coating material therefore suffers irregular surface property, and when the tape is used, it tends to induce generation of substances that stick to the magnetic head. The tendency for such tape degradation to occur not only intensifies with decreasing particle diameter but becomes particularly strong in an acicular magnetic powder composed chiefly of Fe when the magnetic powder contains elements added for the purpose of preventing sintering and/or oxidation, such as Al, Si, Ra (where Ra represents one or more rare earth elements, defined as including Y) and the like.
Thus the inventor became aware of a new problem regarding the development of magnetic powders for enhancing the capacity of magnetic recording media. Specifically, the inventor discovered that progress in increasing the fineness and enhancing the quality of magnetic powders may be accompanied by a decline in the quality of magnetic tapes produced using the magnetic powders. An object of the present invention is to overcome this problem.